Long-term evolution-advanced (LTE-A) networks exploit low-power relay nodes, picocells and femtocells to boost throughput, enhance coverage, decrease latency, and reduce cost. End users in a relay-based LTE-A network can recruit relay nodes to cooperate as virtual antenna arrays, thereby reaping the benefits offered by multiple input single output (MIMO) techniques. Although the relay-based cooperative MIMO (coop MIMO) implementation in LTE-A networks improves performance, security issues are often overlooked. This paper introduces a physical layer security scheme for point-to-point networks, and extends this scheme to MIMO networks. Two practical relay-based coop MIMO architectures and corresponding secret key generation (SKG) schemes are presented. For both the MIMO and coop MIMO networks, the impact of proposed power allocation on SKG rate (SKGR) is quantified via the theoretical and numerical analysis. Results indicate that the proposed power allocation scheme can offer 15%-30% increase in SKGR relative to MIMO/coop MIMO networks with equal power allocation at low-power region, thereby improving network security.

In traditional binary frequency-shift keying (BFSK), two distinct carrier frequencies are used to represent binary data. In this letter, we propose transmitting multiple orthogonal, in-phase subcarriers around two distinct carrier frequencies to represent binary information. The envelope of the resulting FSK signal is a carrier interferometry pattern, and hence, the name carrier interferometry (CI/) FSK. We demonstrate that this technique is spectrally efficient when compared to traditional BFSK. Performance and data-rate benefits are also demonstrated with the use of a novel coherent reception technique. Moreover, while it is difficult to employ traditional BFSK in multipath channels, we show how the new CI/FSK scheme exploits frequency-diversity benefits when used in such channels.

In this letter, a large set of spreading codes that doubles capacity in multicarrier code-division multiple-access (MC-CDMA) systems without any cost in bandwidth and with negligible cost in performance is introduced. This large set is comprised of: 1) complex spreading codes instead of conventional real-valued spreading codes and 2) two sets, each made up of orthogonal complex spreading codes, with minimum cross correlation between sets. Simulations performed over Rayleigh fading channels demonstrate 100% gains in terms of MC-CDMA capacity with negligible loss in performance.

In this paper, a novel merger of multicarrier code-division multiple access (MC-CDMA) and smart antenna arrays is introduced. Here, a group of Q carriers in the MC-CDMA system is applied to its own M-element smart antenna array at the base station (BS). The smart antennas are located in close proximity to one another. We generate a transmit diversity gain at the receiver by carefully moving (oscillating) the antenna array's pattern. The pattern oscillation is achieved by applying appropriate time-varying phases to array elements of each smart antenna. The beam pattern oscillation ensures a mainlobe at the position of the intended user and small oscillations in the beam pattern. This beam pattern oscillation leads to a time-varying channel with a controllable coherence time; hence, a transmit diversity benefit, in the form of a time diversity benefit, is available at the receiver. Employing MC-CDMA with the proposed smart antenna at the BS, we achieve: 1) directionality which creates high network capacity via space-division multiple access; 2) a transmit diversity gain which supports high performance at the receiver in the mobile unit; and 3) increased capacity and performance via MC-CDMA's ability to support both CDMA and frequency diversity benefits, respectively.

This letter provides a novel method for doubling throughput in time division multiple access (TDMA) systems. Specifically, with pseudo-orthogonal positioning of carrier interferometry pulse shapes, a TDMA system is designed to support twice as many real symbols in a slot, without increasing bandwidth or slot duration. With regard to performance, the doubling of throughput comes at the cost of only 1-2 dB performance degradations at probability of error of 10/sup -2/.

In traditional BFSK, two distinct carrier frequencies are used to represent binary '1' and binary '0'. In this paper, we propose transmitting multiple, orthogonal, in-phase sub-carriers around two carrier frequencies to represent the binary information. We demonstrate that this technique is spectrally efficient when compared to traditional BFSK. Performance and data rate benefits are also demonstrated in both non-coherent and novel coherent reception techniques. Moreover, while traditional BFSK is not employed in channels that are frequency selective, we show that with coherent reception, the new FSK scheme can be used in frequency selective channels to exploit frequency diversity benefits.

We merge a smart antenna array with CI/DS-CDMA, a novel implementation of DS-CDMA where chips have a shape referred to as the CI (carrier interferometry) chip shape and are decomposable into N narrowband frequency components. In the antenna array, by applying suitable time-varying phases to the elements, we create small movement (oscillation) in the antenna array's pattern, while steering the main lobe to the position of the intended user. The oscillating antenna pattern creates a time-varying channel with a controllable coherence time. This, in turn, provides transmit diversity in the form of a time diversity gain at the mobile receiver side. Thus, at the receiver, three stages of combining are available: 1) combining time components of the received signal within symbol duration T/sub S/ (each experiencing a different fade) to enhance performance via time diversity; 2) combining frequency components which make up the CI/DS-CDMA chip to enhance the performance via frequency diversity; 3) combining across chips to eliminate interfering users. Employing CI/DS-CDMA with the proposed smart antenna at the base station, we achieve: 1) very high capacity via the merger of SDMA (directionality of antenna array) and CDMA; 2) very high performance via the construction of receivers that exploit both transmit diversity and frequency diversity. We focus on the performance benefits of the proposed system.

This paper proposes a novel scheme which doubles capacity in MC-CDMA systems without any cost in bandwidth and with negligible cost in performance. Specifically: (1) complex spreading codes are used instead of conventional real value spreading codes; and (2) two groups of orthogonal complex spreading codes are used simultaneously, where minimum cross-correlation exists between the two groups. Simulations performed over Rayleigh fading channels using these novel codes demonstrate that the proposed scheme enables gain of 100% in terms of MC-CDMA capacity with negligible performance losses.

We introduce a novel merger of multi-input single-output (MISO) systems and MC-CDMA (multi-carrier code division multiple access) systems. Here, each group of Q carriers in the N-carrier MC-CDMA system (Q

One important requirement for next generation wireless communication systems is the ability to support a wide range of high rate data services. Despite advances in efficient modulation and multiple access technologies, very high data rate transfer will still require ultra-wide frequency bands. Traditional DS-CDMA systems operate over one single continuous bandwidth, and with the limited spectrum available from the FCC auctioned off in small blocks, it will not be possible for DS-CDMA to operate over a contiguous ultra-wide frequency band. This paper demonstrates how a novel chip shaping scheme, designed specifically for DS-CDMA systems, enables DS-CDMA to operate over non-adjacent frequency bands in a way that is identical to its operation if all these bands are made contiguous. The chip shape corresponds to an interferometry pattern created by the superposition of N carriers (adjacent or non-adjacent in the frequency domain). Besides the ability to operate over non-adjacent bands, this novel chip shaping enables DS-CDMA to achieve very high performance by exploiting frequency diversity (instead of path diversity) over the combined bands. With the exception of chip shape and receiver design for operation over non-contiguous bands, this new system retains all the features of a traditional DS-CDMA system.

Airport surface operations (aircraft servicing and maintenance, gate scheduling, and taxi operations) significantly affect the efficiency of airline flight schedules. Therefore, an optimized wireless communication system that supports surface operations can promote airline efficiency. This work presents multipath propagation measurements at airport ramp areas at 5.8 GHz. Statistical characterizations of the wireless channel, from these measurements, indicate large delay spreads (on average 14.78 /spl mu/s) and small coherence bandwidths (0.5 coherence bandwidth on the order of 12.25 Hz). These findings suggest that the radio environment at an airport offers large diversity gains that can be exploited in future spread-spectrum systems.